Mussel meal as substitute for fish meal in the diet of common sole, Solea solea, juveniles enhances growth potential and feed utilization

Common sole Solea solea ongrowing is still a bottleneck for a competitive production of this species and conventional fishmeal (FM) - based diets are often unable to guarantee acceptable performance. The mussel meal (MM), characterized by high palatability and good nutritional value, may represent an innovative ingredient able to enhance the growth potential of this species. Four isoproteic (53%) and isolipidic (11%) pelletized diets were formulated, in which FM was the only protein source (MM0, control diet) or substituted by 25 (MM25), 50 (MM50) and 75% (MM75) MM. Seventy sole juveniles (initial body weight 13 g) per tank were randomly allocated in twelve flat bottom 280-liter square tanks (temperature 20and dissolved oxygen above 7 ppm). Animals were hand-fed twice a day to apparent satiation. Diets were tested in triplicate for 91 days. Performance, carcass indices and liver histology were observed. One-way ANOVA with Tukeys post test were used to analyze data (P < 0.05). Diets containing MM gave significantly higher Specific Growth Rate (SGR) and lower Feed Conversion Rate (FCR) when compared to the control diet. The administration of MM50 and MM75 also resulted in a significantly higher voluntary feed intake (VFI). Whole-body composition was not influenced by dietary treatments. A significant decrease in VSI was observed in fish fed MM50 and MM75 in comparison with the control group. HSI of fish fed MM0 and MM25 was higher than that of fish fed MM75, even though in all the experimental groups liver histology showed a moderate to intense hepatocellular accumulation of lipid or glycogen. According to the results, MM is an effective ingredient for enhancing growth and feed utilization in sole irrespectively to the inclusion levels used in this trial.